负载型VOx／SBA-15催化剂催化CO2气氛下乙苯脱氢反应的研究

利用浸渍法制备了系列不同钒含量的VOx/SBA-15乙苯脱氢催化剂.并采用BET、UV-vis、XRD、TPO和O2脉冲等物理化学表征手段对催化剂进行了表征.二氧化碳气氛下的乙苯氧化脱氢反应结果表明,在550℃,当V2O5的含量为20%时,催化剂表现出最好的脱氢性能.乙苯的转化率达到74.1%,同时也获得95.7%的苯乙烯选择性.20VOx/SBA-15具有较高的比表面积、较多的酸性、较少的积碳,这可能是该催化剂表现出较好的催化性能的原因.     

Ce助剂对V/SiO2催化CO2氧化乙苯脱氢性能的影响

通过N₂吸附、X射线衍射(XRD)、X射线光电子能谱(XPS)、H₂程序升温还原(H₂-TPR)、CO₂程序升温脱附(CO₂-TPD)和热重分析(TGA)等多种表征手段和催化反应性能评价,研究了铈助剂的添加对V/SiO₂催化CO₂氧化乙苯脱氢性能的影响. 结果表明,Ce助剂不仅提高了催化剂活性组分分散性和氧化还原性能,抑制了钒物种的深度还原,而且增强了催化剂碱性和CO₂吸附能力,减缓了积炭生成,从而显著提高了V-Ce/SiO₂对CO₂氧化乙苯脱氢反应的催化活性和稳定性. 在本实验中,V(0.8)-Ce(0.25)/SiO₂催化剂表现出最佳的催化性能,苯乙烯(ST)收率可达55.6%,选择性为98.5%,反应12 h 后,催化剂活性基本不变,与惰性N₂气氛比较,CO₂明显促进了乙苯脱氢反应,归因于CO₂能保持催化剂表面钒物种的高价态.     

CO2气氛下负载型Cr2O3催化剂上乙苯脱氢制苯乙烯反应

 采用浸渍法制备了负载型Cr2O3/Al2O3和Cr2O3/SiO2催化剂,并考察了催化剂在CO2气氛下催化乙苯脱氢制苯乙烯反应的活性. 结果表明,Cr2O3/Al2O3的催化活性高于Cr2O3/SiO2. 这可能是由于Cr2O3在Al2O3载体表面的分散度大大高于在SiO2表面的分散度. 催化剂的催化活性与Cr2O3的负载量有关,在w(Cr2O3)=25%时,Cr2O3/Al2O3的催化活性最高. CO2气氛对乙苯脱氢反应有明显的促进作用; 在CO2气氛下,Cr6+物种可能是催化乙苯脱氢反应活性位的前驱体.     

ZrO2基复合金属氧化物催化剂上CO2温和氧化乙苯制苯乙烯

苯乙烯(SM)是聚合物化学中最重要的单体之一,由其生产的聚合物产品(如PS,SBR和ABS等)具有独特的性能,因而SM的需求逐年增加.乙苯(EB)催化脱氢工艺提供了90％的SM需求,该过程在K促进的氧化铁催化剂上于600-650℃进行.这是一个吸热且体积增大的反应,因此需要绝热反应器和大量的过热过饱和蒸汽以提供热量和降低反应分压,从而有利于反应平衡向SM方向移动,也可避免或消除积碳.同时,也造成大量潜热被浪费;热点也降低了整个反应活性和催化剂寿命.在蒸汽中加入空气或富氧空气,使得副产H2与O2反应,产生的热量可供随后乙苯脱氢反应,同时H2的移除也有利于提高EB单程转化率,并保持高的SM选择性.但是,该过程需要2个催化剂,反应器的设计和催化剂的装填比较复杂,且存在爆炸的危险.因此,人们尝试了多种氧化剂和新型的催化剂.最近也有人提出软氧化剂的概念.这为开发新催化体系提供了可能.相对于O2,CO2的氧化性很弱,但可用作温和氧化剂去除脱氢单元中副产的H2,降低了反应温度,且不影响反应活性和选择性;同时,具有较大的经济性和环保性,在工业上也是切实可行的.除了负载型的碱金属促进的氧化铁催化剂外,各种金属或金属氧化物也用于催化CO2氧化EB脱氢反应中,如Fe,Cr,V和La的氧化物为活性金属,碳材料、MgO、SiO2、Al2O3、Ga2O3、ZrO2、TiO2、水滑石类化合物及分子筛为载体.Park课题组研究了Fe,V和Cr基催化剂,即设计氧化还原的催化剂表面以解离CO2,产生的O用于逆水汽反应.其中以Al2O3负载的V和V-Sb氧化物催化剂性能最为突出;但存在积碳失活和V物种的深度还原等问题.为了进一步提高催化剂性能,该课题组开发了多种ZrO2基复合氧化物催化剂,包括MnO2-ZrO2,TiO2-ZrO2,CeO2-ZrO2和SnO2-ZrO2.这些催化剂具有酸碱特性,在反应中表现出较高的催化性能.因此,本文简要总结了用于CO2氧化EB脱氢反应的ZrO2基催化剂最新研究进展.研究发现,在CO2氧化EB脱氢制SM反应中,CO2在提高催化剂活性和稳定性方面起着非常重要的作用,可被定义为软氧化剂:氧化催化剂表面以保持其表面氧含量,移除催化剂表面产生的积碳和副产物H2,为反应体系提供较高的热容以克服反应平衡限制,从而达到较高的转化率.ZrO2基复合金属氧化物是具有改善的织构特性的纳米粒子,且具有酸碱两性和氧化还原性能.改性可提高催化体系的热稳定性和活性.其中CeO2-V2O5/TiO2-ZrO2催化剂具有恰当的氧化还原性和酸碱两性,二者协同作用,因而催化性能最佳.氧化还原稳定剂Sb的添加进一步提高了其催化性能.碱金属和碱土金属可优化其酸碱性,增加比表面积,从而提高反应活性和选择性以及CO2转化率.继续加强抑制积碳和促进CO2活化方面的研究,可有望进一步提高单程转化率(75％以上)、选择性(98％)和CO2转化率(30％).总之,CO2氧化EB脱氢制SM是一个高度经济性和环境友好的新过程,在未来有望满足SM日益增长的需求.另外,该过程的开发可减少CO2排放,其副产的CO还可用于多种化工过程.然而,该过程仍面临诸多挑战:如何抑制积碳,单程转化率和催化剂寿命有待进一步提高.这些挑战也给我们未来的研究提供了方向.深入理解反应机理、积碳机理和CO2的活化过程也有利于我们开发出更适合工业应用的催化剂.     

钒/钛复合氧化物催化剂用于二氧化碳气氛中乙苯氧化脱氢

 采用改进的酸催化溶胶-凝胶法制备了以TiO2为基体的钛基复合氧化物催化剂, 并将该催化剂用于低温下二氧化碳气氛中乙苯氧化脱氢制苯乙烯反应. 采用X射线衍射、 表面物理吸附、 X射线光电子能谱和热重-质谱等分析手段对反应前后的催化剂进行表征. 结果表明, 催化剂在一定反应条件下具有较好的催化活性. 催化剂失活原因主要是反应过程中产生了积炭和高价钒被还原成低价钒. 反应过程中产生的积炭可以通过空气氧化消除,再生后的催化剂其活性基本上能得到恢复.     

An Overview on the Dehydrogenation of Alkylbenzenes with Carbon Dioxide over Supported Vanadium–Antimony Oxide Catalysts

Utilization of carbon dioxide as a soft oxidant for the catalytic dehydrogenation of ethylbenzene (CO₂-EBDH) has been recently attempted to explore a new technology for producing styrene selectively. This article summarizes the results of our recent attempts to develop effective catalyst systems for the CO₂-EBDH on the basis of alumina-supported vanadium oxide catalysts. Its initial activity and on-stream stability were essentially improved by the introduction of antimony oxide as a promoter into the alumina-supported catalyst. Insertion of zirconium oxide into alumina support substantially increased the catalytic activity. Modification of alumina with magnesium oxide yielded an increase of catalyst stability of alumina-supported V–Sb oxide due to the coking suppression. Carbon dioxide has been confirmed to play a beneficial role of selective oxidant in improving the catalytic performance through the oxidative pathway, avoiding excessive reduction and maintaining desirable oxidation state of vanadium ion (V⁵⁺). The positive effect of carbon dioxide in dehydrogenation reactions of several alkylbenzenes such as 4-diethylbenzene, 4-ethyltoluene, and iso- and n-propylbenzenes was also observed. Along with the easier redox cycle between fully oxidized and partially reduced vanadium species, the optimal surface acidity of the catalyst is also responsible for achieving high activity and catalyst stability. It is highlighted that supra-equilibrium EBDH conversions were obtained over alumina-supported V–Sb oxide catalyst in CO₂-EBDH as compared with those in steam-EBDH in the absence of carbon dioxide.     

Effect of structural,redox and acid characteristics of M<Subscript>x</Subscript>O<Subscript>y</Subscript>/ZrO<Subscript>2</Subscript>(Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) (M-Mn,Co, Cr) oxide nanocomposites on their catalytic properties in the deep oxidation of methane

Alumina-and zirconia-manganese catalysts for the deep oxidation of methane were studied by X-ray phase analysis, temperature-programmed hydrogen reduction, and IR spectroscopy. The most active catalyst has the optimal combination of dimensional, redox, and acid characteristics. The zirconia-manganese catalysts formed on the surface of a kaolin-aerosil honeycomb matrix provides for 80–100% conversion of methane to CO₂ at 690–750 °C. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 6, pp. 367–372, November–December, 2007.     

二氧化碳同环氧丙烷交替共聚用催化剂的研究

探讨了有机金属催化剂的组成及其对二氧化碳同环氧丙烷交替共聚产物结构的影响,发现二乙基锌—助剂体系的催化活性按如次顺序递降:二乙基锌—连苯三酚>二乙基锌—间苯二酚>二乙基锌—对苯二胺>二乙基锌—亚乙基脲。若用三异丁基铝代替二乙基锌同连苯三酚构成催化剂,则失去对二氧化碳同环氧丙烷交替共聚反应的活性同时,著者发现二乙基锌—二元芳胺催化体系与二乙基锌—二元酚催化体系的催化活性规律完全不同。     

纳米Cr2O3系列催化剂上CO2氧化乙烷脱氢制乙烯反应

 采用溶胶－凝胶法和共沸蒸馏法耦合技术制备了纳米Cr2O3催化剂，并采用共沉淀法和共沸蒸馏法耦合技术制备了纳米Cr2O3／Al2O3，Cr2O3／ZrO2和Cr2O3／MgO复合催化剂．应用BET，XRD，XPS，TPR和TEM等物理化学方法对催化剂的结构和物化性质进行了表征，并考察了该系列催化剂上CO2氧化乙烷脱氢制乙烯的反应性能．结果表明，纳米Cr2O3催化剂上乙烷和CO2的转化率均明显高于常规Cr2O3催化剂，但乙烯的选择性低于常规Cr2O3催化剂；纳米复合催化剂中的复合成分显著影响催化剂的催化性能．其中，10％Cr2O3／MgO纳米复合催化剂在温度为973K时，乙烷转化率和乙烯选择性分别可达到61．54％和94．79％．纳米催化剂表面Cr的还原性以及Cr6＋／Cr3＋比值是影响乙烷转化率和乙烯选择性的重要因素．     

Interaction of Cl<Subscript>2</Subscript> and SO<Subscript>2</Subscript> with Finely Divided In<Subscript>2</Subscript>O<Subscript>3</Subscript>

The effect of O₂, Cl₂, and SO₂ on electrophysical and sorption properties of powdered In₂O₃ with a large specific area is studied at 23–200°C. The specimen is most sensitive to Cl₂ and SO₂ at near-room temperatures.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 529–536.Original Russian Text Copyright © 2005 by Vinokurova, Derlyukova.     

Synthesis characterization and catalytic evaluation of Ni/ZrO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> aerogels catalysts

The Ni/ZrO₂/SiO₂ aerogels catalysts were synthesized via three different routes: (i) impregnation ZrO₂–SiO₂ composite aerogels with a aqueous solution of Ni(NO₃)₂, (ii) impregnation SiO₂ aerogels with a mixed aqueous solution of Ni(NO₃)₂ and ZrO(NO₃)₂ · 2H₂O, (iii) one-pot sol–gel procedure from precursors Ni(NO₃)₂/ZrO(NO₃)₂ · 2H₂O/Si(OC₂H₅)₄. These catalysts were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), ammonia temperature-programmed desorption (NH₃-TPD), N₂ adsorption–desorption isotherms and Fourier transform infrared (FT-IR). The Liquid-phase hydrogenation of maleic anhydride (MA) was performed over these catalysts. The results revealed that the different preparation routes result in a difference between the obtained samples, concerning the crystal structure and composition, surface acidity, mixed level of each component, texture, and catalytic selectivity.     

天然气和二氧化碳转化制合成气的研究 Ⅴ．甲烷脱氢积炭反应特征

采用ＴＧ、ＸＲＤ、ＳＥＭ、ＥＤＡＸ和脉冲色谱技术，研究了Ｎｉ／Ａｌ２Ｏ３和Ｎｉ／ＡＲＭ催化剂的甲烷脱氢积炭反应特征。结果指出，甲烷脱氢反应的积炭行为与催化剂上镍的分散状态有关。Ｎｉ－２催化剂上Ｎｉ的分散度小，晶粒大，甲烷脱氢形成的炭丝较长，主要以石墨型炭游离存在：而Ｎｉ／ＡＲＭ催化剂上Ｎｉ的分散度大，镍晶粒小，甲烷脱氢形成的炭丝较短，主要覆盖在催化剂活性中心表面。甲烷脱氢主要产生无定型炭和石墨型炭，其中无定型炭可以被ＣＯ２部分消除。在催化剂制备时，通过提高镍在催化剂表面的分散度，减小镍的晶粒大小，不仅可以提高催化剂的活性，而且可以提高ＣＯ２对积炭的消炭性能。     

Surface Acidity/Basicity and Catalytic Reactivity of CeO2/γ-Al2O3 Catalysts for the Oxidative Dehydrogenation of Ethane with Carbon Dioxide to Ethylene

Dehydrogenation of ethane to ethylene in CO2 was investigated over CeO2/γ-Al2O3 catalysts at 700 ℃ in a conventional flow reactor operating at atmospheric pressure. XRD, BET and microcalorimetric adsorption techniques were used to characterize the structure and surface acidity/basicity of the CeO2/γ-Al2O3 catalysts. The results show that the surface acidity decreased while the surface basicity increased after the addition of CeO2 to γ-Al2O3. Accordingly, the activity of the hydrogenation reaction of CO2 increased, which might be responsible for the enhanced conversion in the dehydrogenation of ethane to ethylene. The highest ethane conversion obtained was about 15% for the 25%CeO2/γ-Al2O3. The selectivity to ethylene was high for all the CeO2, γ-Al2O3 and CeO2/γ-Al2O3 catalysts.     

Influence of the composition of carriers based on ZrO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> on the properties of cobalt-containing catalysts on the selective reduction of NO with methane

A series of cobalt-containing granulated and structured catalysts based on zirconium and aluminum oxides has been studied. The optimum composition of binary oxide samples (80% ZrO₂ − 20% Al₂O₃) for the selective reduction of nitrogen monoxide with methane (84% conversion of NO achieved at 320 °C) has been determined. The activity of the structured catalysts depends on both the composition of the secondary carrier (ZrO₂, Al₂O₃, and their mixture) and on the nature of the skeleton of the cellular structure (cordierite, kaolin-aerosil). __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 237–241, July–August, 2007.     

Dehydrogenation of Isobutane to Isobutene with Carbon Dioxide over SBA‐15‐Supported Chromia‐Ceria Catalysts

A series of SBA‐15‐supported chromia‐ceria catalysts with 3% Cr and 1%–5% Ce (3Cr‐Ce/SBA) were prepared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N₂ adsorption, SEM, TEM‐EDX, Raman spectroscopy, UV–vis spectroscopy, XPS and H₂‐TPR, and their catalytic performance for isobutane dehydrogenation with CO₂ was tested. The addition of ceria to SBA‐15‐supported chromia improves the dispersion of chromium species. 3Cr‐Ce/SBA catalysts are more active than SBA‐15‐supported chromia (3Cr/SBA), which is due to a higher concentration of Cr⁶⁺ species present on the former catalysts. The 3Cr‐3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570 °C after 10 min of the reaction.     

pH-sensing properties of PbO<Subscript>2</Subscript> thin film electrodeposited on carbon ceramic electrode

In this paper, a new highly sensitive potentiometric pH electrode is proposed based on the solid-state PbO₂ film electrodeposited on carbon ceramic electrode (CCE). Two different crystal structures of PbO₂, α and β were examined and the similar results were obtained. Moreover, the experimental results obtained for the proposed pH sensor and a conventional glass pH electrode were in good agreement. The electromotive force (emf) signal between the pH-sensitive PbO₂-coated CCE and SCE reference electrode was linear over the pH range of 1.5–12.5. Near-Nernstian slopes of −64.82 and −57.85 mV/pH unit were obtained for α- and β-PbO₂ electrodes, respectively. The interferences of some mono-valence and multi-valence ions on potentiometric response of the sensor were studied. The proposed pH sensor displayed high ion selectivity with respect to K⁺, Na⁺, Ca²⁺, and Li⁺, with log values around −12 and has a working lifetime of about 30 days. Key parameters important for the pH sensor performance, including kind of PbO₂ film, selectivity, response time, stability, and reproducibility, have been characterized. The proposed electrode showed a good efficiency for direct pH-metry after calibration and pH-metric titrations without calibration step. The response time was about 1 s in acidic medium and less than 30 s in alkaline solutions. The pH values of complex matrix samples such as fruit juices measured by the proposed sensor and a conventional glass pH electrode were in good agreement.     

Photoelectrochemical processes at interfaces of nanostructured TiO<Subscript>2</Subscript>/carbon black composites studied by scanning photoelectrochemical microscopy

The local photoelectrochemical response of TiO₂/carbon black photocatalysts was studied by means of scanning photoelectrochemical microscopy performed under UV illumination and external polarization. Catalysts obtained by sol-gel techniques showed a uniform response that improved under anodic polarization, in contrast to the non-uniform response of mixtures that show enhancement under cathodic polarization. To explain the differences in photoelectrochemical activity, we performed electrochemical and capacitive studies under dark condition, finding a larger positive shift in the rest potential of sol-gel composites plus evidence of Fermi-level pinning. We propose the last is related to the presence of carbon states with a strong acceptor character formed during the sol-gel synthesis. An energy band diagram of the composites were sketched based on the data obtained.     

Effect of ZrO<Subscript>2</Subscript> morphology in copper–cerium–zirconium oxide systems on their catalytic properties in the reaction of co oxidation in hydrogen-rich mixtures

We studied the catalytic properties of copper–cerium oxide systems, deposited on supports obtained by calcination of yttrium-stabilized zirconium dioxide at 300-1000 °C, in the reaction of selective oxidation of CO in a stream of hydrogen. We have shown that the catalytic activity of the samples obtained correlates with the activity of the original supports in the reaction of CO oxidation: the highest CO conversion is observed on catalysts with the highest and the lowest specific surface area. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 115-120, March-April, 2009.     

Characterization of nanosized ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel synthesized by the sol–gel method

Single-phase zinc aluminate (ZnAl₂O₄) nanoparticles with the spinel structure was successfully obtained by the sol–gel method. The nanoparticles are crystalline with no impurities related to ZnO or Al₂O₃ residues. The microstructural environment of aluminum ions changes with heat treatment temperature, as observed by FT-IR and also by ²⁷Al solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectra. The photoluminescence spectra show that the emission of pristine ZnAl₂O₄ may change depending on the calcining temperature due to the quantum size effect.     

Structure and Catalytic Properties of Ceria-based Nickel Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina. The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance also depends on the crystal structure of Ni–Ce–ZrO₂. For example, nickel catalysts co-precipitated with Ce_0.8Zr_0.2O₂ having cubic phase gave synthesis gas with CH₄ conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO₂ having tetragonal phase (Ce_0.8Zr_0.2O₂) or mixed oxide phase (Ce_0.5Zr_0.5O₂) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst is attributed to a combination effect of nano-crystalline nature of cubic Ce_0.8Zr_0.2O₂ support and the finely dispersed nano size NiO _x crystallites, resulting in the intimate contact between Ni and Ce_0.8Zr_0.2O₂ particles. The Ni/Ce–ZrO₂/θ–Al₂O₃ also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO₂ resulting in the existence of stable NiO _x species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results further confirmed that NiO _x formation was more favorable than NiO or NiAl₂O₄ formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support. Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO₂/CH₄ ratio and H₂O and/or O₂ addition were also examined.